WASHINGTON'S dog days of August: not a bad time, it would seem, for an all-day blues festival. Saturday at noon the second annual "Blues Bash" gets underway at the county equestrian center in Upper Marlboro. Appearing this year will be singer Jimmy Witherspoon, guitarists Johnny Copeland and Elvin Bishop, pianist Pinetop Perkins, harmonica ace Jerry Portnoy and numerous others, including much local talent. For those more apt to enjoy the music indoors, as the air conditioner hums merrily along in the background, here's a roundup of several new blues releases by others.

JAMES COTTON --

"Take Me Back" (Blind Pig BP 2587). A sentimental journey and quite a departure for Mr. Superharp, this album sets out to depict various shades of early post-World War II blues. Some of the tunes reflect styles that have always played a part in Cotton's development. His version of "Dust My Broom" for example, recalls Sonny Boy Williamson's early influence on him. Yet the album also includes a couple of laconic Jimmy Reed blues which are just as convincing and a lot more refreshing. What's more, the backing by Pinetop Perkins and a cast of seasoned Chicago bluesmen is first-rate.

HUBERT SUMLIN --

"Hubert Sumlin's Blues Party" (Black Top BT 1036). Bringing guitarist Hubert Sumlin back into the studio was a geat idea, but teaming him up with vocalist Mighty Sam McClain was an inspired one. No great shakes as a singer himself, Sumlin wisely defers to McClain's smoldering baritone most of the time. In turn, McClain delivers the album's most powerful performance. Particularly impressive is "A Soul That's Been Abused," an intimate ballad that instantly recalls Bobby Bland's best work. Sumlin, best known for his years with Howlin' Wolf, still plays like no one else, favoring odd accents and jagged lines. He can be downright spooky at times, as his eerie tribute to Wolf on "Living the Blues" demonstrates.

SNOOKS EAGLIN --

"Baby, You Can Get Your Gun" (Black Top BT 1037). Like a lot of blues musicians, this New Orleans guitarist has been poorly served by recordings over the years. This time around he's gone into the studio with a strong band, featuring keyboardist Ron Levy and guitarist Ronnie Earl, and a surprisingly diverse if not always first class collection. "Profidia," for instance, is a terrific tribute to the Ventures, and really displays Eaglin's remarkable range as a guitarist. Shuffle tunes like "Oh Sweetness" roll with rhumba rhythms and the headlong momentum of a good Professor Longhair arrangement, and Eaglin even manages to detonate some James Brown funk on "Drop That Bomb!"

SNOOKY PRYOR --

"Snooky" (Blind Pig BP 2387). Pryor's on-and-off career (mostly off in recent years) hasn't diminished his interest in Chicago postwar blues or his talent for playing it. Like Cotton, he was strongly influenced by Sonny Boy Williamson, both in singing and harmonic playing. And yet, while Williamson's presence is clearly felt on all of these performances, Pryor's own personality is what puts them over. Occasionally he falters -- "It Hurts Me Too" suffers from a perfunctory vocal -- but more often Pryor sings with simple honesty and underscores his words with a pungent refrain from his harmonica.

BIG TWIST AND THE MELLOW FELLOWS --

"Live From Chicago! Bigger Than Life!!" (Alligator AL 4755). Despite the impressive horn section that powers the Fellows and Larry "Big Twist" Nolan's imposing voice, this live album opens with an oddly unmoving fanfare called "The Sweet Sound of Rhythm and Blues." It then takes half of the first side of the album for the band to build up a good head of steam (finally attaining it, coincidentally, on "Steamroller Blues"). The rest of the album has its ups and downs as well, which may explain why the crowd reaction sounds so muted. Tunes like "Too Much Barbecue" obviously allow for some entertaining antics on stage, but listening to the record you're left with one very distinct feeling: You had to be there.